Electrical transformer ballast



June 18, 1957 S I ---L \D c. E. STRECKER 2,796,554

ELECTRICAL TRANSFORMER BALLAST Filed July 25. 1952 A Inventor:- CharlesE. Strecker;

y WWQ His Attorney.

United States Patent ELECTRICAL TRANSFORMER BALLAST Charles E. Strecker,Fort Wayne, Ind, assignor to General Electric Company, a corporation ofNew York Application July 25, 1952, Serial No. 300,916

Claims. (Cl. 3'15--97) This invention relates to electrical transformerballasts and has for an object the provision of a novel, simple andeconomical high reactance transformer ballast for a plurality ofserially connected electric arc discharge devices such as fluorescentlamps.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

Referring now to the single figure of the accompanying drawing, whichillustrates diagrammatically an embodiment of the invention, the highreactance transformer ballast is indicated generally at 1 and it isshown connected to two hot cathode fluorescent lamps 2 and 3, which arepreferably of the co-called rapid start type as described and claimed inU. S. Patent 2,774,918 granted December 18, 1956, upon an application,Serial No. 250,106, filed Oct. 6, 1951, in the name of Eugene Lemmersand assigned to the same assignee. They are characterized by havingcathodes which can be continuously heated to electron emission atvoltages below the ionization voltage of the gas or vapor in the lamp.The transformer ballast is enclosed in a metal case which is indicatedschematically at 4- and comprises essentially a shelltype transformercore and coil assembly 5 and associated electric circuit elementsincluding a starting capacitor 6, a running capacitor 7 for providingleading current operation, and interconnecting circuit conductors.

The core of assembly 5 comprises a laminated magnetic core preferably ofthe general type described in U. S. Patent 2,734,176 granted February 7,1956 upon an application, Serial No. 239,229, filed July 30, 1951, inthe names of Herbert R. Gould and Andrew Schevtchuk and assi ned to thesame assignee. It has three lamination pieces or punchings perlamination layer, there being in each layer a central winding legpunching 8 and similar three-legged yoke punchings 9 disposed onopposite sides of the winding leg punching with the two end legs of eachyoke punching in contact with the winding leg punching. Between thecenter part of the winding leg punching on opposite sides under thecenter legs .of the yoke punchings 9 are non-magnetic gaps for highreluctance leakage flux paths or magnetic shunts of the transformer,which paths include the center legs of the yoke punchings 9. The termmagnetic shunt is used herein to mean a high reluctance path formagnetic leakage flux whether through magnetic material or throughnon-magnetic material such as air. The right hand end legs of the yokepunchings 9, as viewed in the drawing, are notched so as to contact onlythe corners of the leg punching 8 and provide gaps 10 and magneticbridges 11 therefor which are buried in the core, i. e., separated fromcase 4 by the right hand end legs of yoke punchings 9. Also, theleft-hand end legs are shorter than the right hand end legs of thepunchings for permitting economical nesting of these punchings' whenthey are produced.

Mcunted on the .center leg punchings .8, on opposite sides of the centerlegs of the yoke 'punchings'9, are a pri- 2,795,554- Patented June 18,1957 2 mary winding 12 and a secondary winding 13, the primary windinghaving a tap 14. Also mounted on the winding leg -9 adjacent to orclosely coupled to primary winding 12 are a pair of cathode heatersupply windings 15 and 16.

The circuit elements of the transformer ballast are connected to eachother and to the lamps and to suitable input terminals 17 in thefollowing manner. The primary winding 12 is connected directly betweenthe input terminals by way of conductors 18, 19, tap 14, conductors 20and 21. The secondary winding 13 has one terminal 22 thereof directlyconnected to the conductor 18 so that the primary winding and thesecondary winding are connected in autotransformer relationship, and thepolarity of the windings is such that the connection produces voltagestep-up action. The other terminal 23 of the secondary winding 13 is thehigh voltage terminal .of the step-up autotransfo-rrner and this highvoltage terminal or conductor 23 is connected to one terminal or cathodeheater of the lamp 3 by way of the running capacitor 7 and a conductor24. The electrically adjacent electrodes or cathode heaters of the lamps2 and 3 are directly interconnected as shown, and the left-hand end ofthe lamp 2 is connected to the low voltage or normally grounded terminalof the transformer by a conductor 26 so that the full voltage of thewindings 12 and 13 in series is impressed across the lamps 2 and 3 inseries.

For insuring proper distribution of the sum of the open circuit outputvoltage of the windings 12 and 13 across the lamps 2 and 3, one of thelamps, for example the lamp 3 is permanently shunted by the startingcapacitor 6. This is not in all cases essential, as the distributedinherent capacities of the circuit elements including-the windings andthe lamps themselves, will in certain cases provide proper distributionof voltage. However, for best and most reliable results, it ispreferable to employ the starting capacitor 6, which may be connectedacross either lamp. For suppressing radio frequency disturbancesproduced by the arc discharges in the lamps 2 and 3, the two lamps maybe shunted by a radio interference suppressing capacitor (not shown).

For supplying heating current to a cathode 28 of lamp 2 this cathode isconnected by way of a conductor 29 to the remaining terminal of theprimary winding and thence by way of the tap 14 back to the other sideof the cathode 28 through conductors 20, 21 and 26. One side of cathode39 of the lamp 3 is connected by way of a conductor 31 to the winding 16and then by way of conductors 32 and 24- back to the other side of thecathode 30.

The electrically adjacent ends of cathodes 33 (of lamp 2) and 34 (oflamp 3) are preferably energizedin parallel from the winding 15, thecircuit connections being from the left hand end of winding 15 through aconductor 27, the cathodes 33 and 34 in parallel, conductor 25 and backto winding 15. Winding 15 has as many turns as winding 16 and as manyturns as there are between tap 14 and terminal conductor 29 of theprimary winding 12.

The operation of the illustrated embodiment of the invention is asfollows:

When the input terminals 17 are connected to a suitable source of supply(not shown) the full open circuit voltage, which is the sum of thevoltages of the primary winding 12 and secondary winding 13, isimpressed across the lamps 2 and 3 in series. However, the capacitanceof starting capacitor 6 is very much greater than the inherentcapacitance of the lamps 2 and 3 so that practically all of the outputvoltage appears across the lamp ,2 andvery little of this voltage is atfirst impressed across the lamp 3 and the capacitor 6 in parallel. Atthe same time the cathode 28 is energized by the voltage of the winding12 between tap 14 and terminal 29, the cathode 30 is .ener

gized by the voltage of the winding 16 and the cathodes 33 and 34 areenergized in parallel by the voltage of the winding 15 so that thecathodes are quickly heated to electron emitting temperature. As soon asthe cathodes of the lamp 2 emit electrons the starting voltage of thelamp 2 is reduced very much below the voltage which would be required tostart it or cause an arc discharge between its electrodes 28 and 33 ifthey were cold. Therefore, the secondary winding 13 can have a very muchlower voltage, and consequently a fewer number of turns than would berequired if the lamps were to be started by means of a cold cathodedischarge, and the combined voltages of the windings 12 and 13 need onlybe a little more than sufficient to start the lamp 2 with its cathodes30 and 34 hot and emitting electrons. As soon as the lamp 2 starts, thedischarge current in the lamp 2 flows through the starting capacitor 6,thus producing a relatively high voltage drop in the capacitor 6, whichvoltage drop is impressed across the lamp 3 and causes the lamp 3 toform an arc discharge between its heated terminal electrodes or cathodes30 and 34. After the lamp 3 starts, the arc drop in the lamp 3 falls toa relatively low value, so that the capacitor 6 is effectively shortcircuited by the lamp 3.

The ballasting action, so as to limit the operating cur rent of thelamps to the proper value, is obtained by means of the running capacitor7 and the leakage reactance of the transformer which is produced by thecenter 'legs of the yoke members 9, which act as part of the magneticshunts in the core between the primary winding 12 and the secondarywinding 13. In other words, when the lamps are in operation the leadingphase of the lamp current, resulting from capacitor 7, in flowingthrough the secondary winding 13 produces a magnetizing efiect in thecore, and the resulting excess flux over the magnetizing flux producedby the primary winding 12 flows largely through the magnetic shunts in alocal magnetic circuit which causes the main secondary winding section13 to act as a current limiting reactor to a large extent.

The bridged gaps Hi -11 serve to limit the excess leading leakage fluxof the secondary winding so as to prevent magnetic saturation of thepart of the core occupied by the secondary winding. As they are buriedin the core, i. e. formed in the internal portion of the core and not onthe outside, they have very little stray flux which gets outside thecore to cause noise and heating in the usual surrounding metal case.

As an example of a specific transformer ballast in accordance with thisinvention which is suitable for operating two 40-watt fluorescent lampsin series, the core may be 4 inches long and 2% inches wide with a stackheight of inch of laminations of 19 to 25 mils thickness. The windingleg 8 may be one inch wide, the length of the primary winding section ofthe core may be 1 inches and the length of the secondary winding sectionof the core may be 2 inches. The primary winding 12 may consist of S49turns with the tap 14 located at 5 32 turns, the secondary winding 13may consist of 1222 turns, the winding 15 may consist of 17 turns andthe winding 16 may have 17 turns. The starting capacitor 6 may have .05microfarad capacity and the running capacitor 7 may have 2.85microfarads capacity. The power factor with both lamps operating isabout'96% leading.

While there has been shown and described a particular embodiment of theinvention, it will be obvious to those skilled in the art that changesand modifications can be made without departing from the invention, andtherefore it is aimed in the appended claims to cover all such changesand modifications as fall within the true spirit and scope of theinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A high reactance transformer ballast for a plurality of seriallyconnected arc discharge devices comprising,

in combination, a substantially closed magnetic core having a primarywinding section and a secondary winding section separated by a magneticshunt for leakage flux from said sections, a buried bridged gap in saidcore adjacent said secondary winding section, a primary winding on theprimary core section and a secondary winding on the secondary coresection, said primary winding and said main secondary winding beingconnected in voltage step-up autotransformer relation for supplyingstarting voltage and operating current to a plurality of are dischargedevices in series, and a plurality of cathode heating supply windingsmounted on said primary core section only.

2. A high reactance transformer ballast for starting and operating withleading current a pair of serially connected hot cathode fluorescentlamps comprising, in combination, a shell-type transformer core having acentral winding leg and oppositely disposed three-legged yoke memberswith the outer legs of the yoke members in contact with opposite sidesof the winding leg member and with the intermediate legs of the yokemembers spaced from the winding leg so as to constitute relatively highreluctance magnetic shunts which divide the winding leg into a primarywinding section and a secondary winding section, the end legs of theyoke members which contact said secondary winding section of the windingleg being notched so as to produce buried bridged gaps therebetween, aprimary winding comprising a main primary section separated by a tapfrom an integral extended cathode heating supply section on the primarywinding section of the core winding leg, a secondary winding on thesecondary winding portion of the core winding leg, a pair of cathodeheating supply windings mounted on the primary winding section of thecore winding leg, :a running capacitor, said main primary windingsection and said secondary winding being connected in voltage step-upautotransformer relation in series with said running capacitor forsupplying starting voltage and leading operating current to a pair ofserially connected hot cathode fluorescent lamps, starting capacitor forconnection in shunt circuit relation with one of said lamps, saidstarting capacitor having a substantially greater capacitance than thelamp across which it is adapted to be connected, one cathode heatersupply winding on the primary winding section of the core winding legbeing connected for supplying heating current to electrically adjacentcathodes of different ones of said lamps, said starting capacitor havingone terminal connected to one side of said one cathode heating windingand having its other terminal adapted to be connected to the othercathode of one of said lamps the extended primary winding section ofsaid primary winding being connected for supplying heating current tothe other cathode of the lamp which is adapted to be connected to themain primary winding, the remaining cathode heating supply winding onthe primary winding section of the core winding leg being connected forsupplying cathode heating current to the remaining cathode of the otherlamp which is for connection directly to the main secondary winding.

3. A high reactance transformer ballast for a pair of serially connectedrapid start fluorescent lamps comprising, in combination, asubstantially closed magnetic core having a primary winding section anda secondary winding section which are separated by at least onerelatively high reluctance magnetic shunt, said core-also 'having aseries buried bridged gap adjacent said secondary winding section, aprimary winding on said primary section and a secondary winding on saidsecondary winding section, a running capacitor, said primary winding andsaid secondary winding being connected in voltage step-upautotransformer relationship in series with said running capacitor forsupplying starting voltage and leading operating current to Ia pair ofserially connected soft start fluorescent lamps, a starting capacitorfor connection across one of said lamps, a metal case enclosing saidtransformer and capacitors,'and three cathode heating supply windings onsaid primary Winding core section, one of the cathode heating supplywindings which supplies the cathode for the lamp electrode which is forconnection to the primary winding being integral with said primarywinding, one of the other cathode heating supply Windings having thesame number of turns as said supply Winding which is integral With saidprimary winding and being for the cathode of the other lamp which isconnected to said secondary winding, and the remaining cathode heatingsupply Winding having as many turns as the others and being forenergizing the remaining two cathodes in parallel, said startingcapacitor having one terminal connected to one side of said remainingcathode heating supply Winding and its other terminal adapted to beconnected to one of said first two lamp cathodes.

4. The high reactance transformer ballast of claim 1 comprising arunning capacitor connected in series with said secondary winding.

5. The high reactance transformer ballast of claim 4 comprising astarting capacitor connected between two of said cathode heating supplywindings for connection across one of said are discharge devices.

References Cited in the file of this patent UNITED STATES PATENTS2,496,981 Boucher Feb. 7, 1950 2,504,549 Lemmers Apr. 18, 1950 2,558,293Feinberg June 26, 1951

